1. Field of the invention
The invention relates to a device for working sheet-like material, such as a press brake for bending steel sheet.
2. Description of Related Art
Press brakes used for working sheet-like materials are well known from the prior art. When the article to be bent is delivered with the center of the axis of the article to be bent at a position in the center of the beams (symmetric pressing), the pressure is equally distributed along the pressing axis of this article. When the article is delivered with the center of the axis of the article to be bent away from the center, an unequal distribution of pressure will result, with lower pressures towards the longitudinal ends of the pressing beams. The unequal distribution of pressure will cause the beams to become unstable and tilt. Delivery positions away from the center are often preferred for bending materials with a small surface (asymmetric pressing) because of the limited pressures exerted at the longitudinal ends of the beams.
Press brakes from the prior art are often employed with at least two separate sets of driving means in each movable beam, having the ability to turn off the pressure selectively, for instance by only applying pressure with the half of the upper beam to which the article is delivered. Still, in many cases, pressure is exerted asymmetrically relative to the position of the article, causing instability and tilting.
It is known to use spring means to urge the beams away of each other. The use of these spring means would reduce or prevent tilting in the case of asymmetric pressing, but would result in lowering the maximum pressure for folding and reducing the efficiency of the device in the case of symmetric pressing.
It is an object of the invention to reduce or even remove the above-mentioned disadvantages of the prior art.